Study of Contact Parameters in Metal-on-plastic Hip Endoprothesis with a New Analytical Method of Contact Mechanics

Prezented the author proposes a computional method for calculating contact parameters (i.e., maximum contact pressures, angle and diameter of contact) in the hip prosthesis made of thermo-diffusion nitrided (TDN) Grade 2 and ultra-high molecular weight polyethylene (UHMWPE). The impact has been investigated of hip joint load, prosthesis head diameter and radial clearance on the above contact parameters. Relationships between maximum contact pressures and the above-mentioned contact parameters are determined. Both increasing radial clearance and endoprosthesis loading cause a linear increase in contact pressure. However, when the head diameter increases, there is a non-linear reduction of contact pressure. The contact diameter increases linearly as the head diameter increases. It is known that the Young's modulus of UHMWPE can differ up to about 3 times. So the analysis of the influence of both Young's modulus and Poisson's ratio on the maximum contact pressure was carried out. According to the given method, the endoprosthesis with non-spherical surfaces of its elements was also tested (Alpharabola geometry). An analysis of the effect of head deviation from sphericity in the form of oval on contact pressure, contact angle and contact diameter was performed. Beneficial effects of this geometry were determined.